The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present invention but provided by the invention. Some such contributions of the invention may be specifically pointed out below, whereas other such contributions of the invention will be apparent from their context.
One special feature offered in mobile communication systems is group communication. The term “group”, as used herein, refers to any logical group of two or more users intended to participate in the same group communication. Examples of group communication include a conference call and a group call, which is a call in which one or more participants may take turns to speak and to listen to each other.
Conventionally, conference calls between three or more participants established such that each participant calls to a bridge, have been available in public switched communication systems. On the other hand, group communication in which one participant calls to the group and the others are called to has been available only in trunked mobile communication systems, such as Professional Mobile Radio or Private Mobile Radio (PMR) systems, such as TETRA (Terrestrial Trunked Radio), which are special radio systems primarily intended for professional and governmental users. Thanks to the evolvement of communication technology, particularly IP-based communication technology, and end user terminals, more enhanced group communication services are now available also in public mobile communication systems. An example of such a service is Push-to-talk over Cellular (PoC), which allows user voice communications to be shared with a single recipient (1-to-1) or between groups of recipients, as in a group chat session (1-to-many) over mobile networks. The PoC service is implemented such that a PoC server, or a server system, receives voice from one participant in the conversation and sends it to other participants in the session.
The main group types are a pre-arranged group, an ad hoc group or a chat group; other group types are subtypes of the above. A pre-arranged group, sometimes called a pre-defined group, is a group having predefined characteristics and group members, and a server hosting the group invites other group members when a first member joins a group session, i.e. sends, using a URI (uniform resource identifier) of the pre-arranged group, to a server hosting the pre-arranged group, an invitation to the group or a request to establish a session with the group. A chat group differs from the pre-arranged group in such a respect that each member individually joins and leaves the group session, and thereby the server hosting the chat group does not invite other members to join. When a member joins a chat room, he/she sends an invitation to a URI of the chat group. An ad hoc group is a group whose intended participants are selected by a group creator, who sends to a server providing ad-hoc services, indications of participants in a request to establish an ad hoc group session. The request is sent using an URI of the server, or a corresponding service in the server, and the server invites the participants who were indicated in the request to join the session. The ad hoc group does not necessarily have predefined characteristics; they may be negotiated during the group establishment.